Satellite communication technology includes the transmission of radiofrequency signals from a satellite directly to antennas arranged at end-user premises. Such type of transmission is sometimes referred to as direct-to-home (DTH) satellite transmission, and usually implies the use of a satellite dish reflector with a low noise block (LNB) receiver. The satellite may for instance be a geostationary satellite orbiting the earth. Direct-to-home (DTH) satellite transmission offers specific advantages while involving specific technical requirements and challenges.
The use of direct-to-home (DTH) satellite communications offers the following advantages. No terrestrial channel, such as a cable or wire, is required to provide communication to the end-user premises so that broadcast transmission can take place to virtually every place on earth. The use of high frequency signals in a line-of-sight (LOS) manner may provide high bandwidth and transmission rate communication.
Direct-to-home (DTH) satellite communications also involve specific technical requirements and challenges. The receiving antenna's reflector must be as small as possible, to minimise the visual and aesthetic impact of the reflector without impairing quality of reception. Therefore, the receiving apparatus interacting with the reflector must be as efficient as possible, so as not to affect the signal quality. The receiver should also be as simple as possible to reduce its cost. At the same time, the setting up and adjustment of the orientation of the receiving antenna at the end-user side should be as easy as possible and the receiver should have a high tolerance to pointing errors.
Radiofrequency signals broadcasted from satellites are often linearly polarized, for reuse of frequency bandwidth. That is, two orthogonally polarized signals on the same bandwidth are transmitted from the satellite. Misalignment of the polarization reception elements of the antenna and the polarization of the incoming signal affects the signal quality and is therefore undesirable.
One way to avoid misalignment of the polarization reception elements of the antenna with respect to the polarization of the incoming signal is by mechanically rotating, i.e. tilting, the receiver to align the receiving elements with the polarization of the incoming signal. This usually requires either delicate manual adjustment procedures or relatively expensive electromechanical means for rotating the receiver. Such electromechanical steering means, which should usually be adapted for outdoor environments, i.e. arranged by the satellite antenna, may be subject to mechanical failures. Another way to cope with a misalignment of the polarization reception elements and the polarization components of the incoming signal is by using electronic means.
U.S. Pat. No. 5,568,158 discloses an electronically adaptable polarization antenna feed apparatus. An electronic circuit is adapted to the apparatus for reception of polarized radiofrequency (RF) signals. Through the use of a combiner and variable gain amplifiers or attenuators, the signals from two orthogonally polarized signal paths are combined such that a maximum signal-to-noise ratio is obtained for a desired polarization.
There is a constant need for improving such apparatus in view of the above-mentioned technical requirements and challenges, including, but not limited to, antenna pointing accuracy and polarization alignment.